1. Field of the Invention
The present invention relates to a new tubular lining material for pipe lines, especially underground pipe lines having a relatively large inner diameter, which comprises a specific tubular textile jacket overlaid on the external surface thereof with an air-impervious coating of a flexible synthetic resin. More particularly, the present invention relates to a new tubular lining material for pipe lines which comprises a tubular textile jacket made of crimped yarns of polybutylene terephthalate fibers as warps and a crimped yarn of synthetic fibers as the weft knitted or woven in a tubular form overlaid with an air-impervious coating of a flexible synthetic resin and which is suitable for reinforcing underground pipe lines such as gas conduits, city water pipes, sewage pipes, petroleum pipe lines and pipes enclosing power transmission wires or telecommunication cables.
2. Description of the Prior Art
From the past, superannuation or damage of underground pipe lines often causes dangerous leakage of combustible fluids or electricity and unexpected flood, thus resulting in accidents and traffic disturbance. When such pipe lines are buried in the ground, damage of the underground pipe lines caused by external force or superannuation will induce an extremely dangerous burst of gas or water. Especially, in case of rupture of the underground pipe lines caused by superannuation, it usually occurs suddenly and is not predictable. On the other hand, only one effective countermeasure in the past was available to prevent such troubles which was to dig up the superannuated or damaged pipe lines over the respective length in the order of several ten or hundred meters for replacing them with new ones. During this pipe-exchange work, people experience much trouble since supply of gas, city water or fuel is discontinued and even traffic is limited where the pipe lines are buried below the public roads. In this case, much labor and cost are required for the pipe-exchange work in addition to the difficulty in the work itself. Under such circumstances, a pipe-lining method was proposed for attaining the purpose of repairing damaged portions of the pipe lines or previously reinforcing them so as to withstand mechanical shock. This pipe-lining method attracted commercial interest at the time because there was no necessity of digging up the pipe lines already constructed. In this method, however, the treatment for lining pipe lines is rather primitive and the step for inserting a flexible plastic tube into the underground pipe lines is extremely difficult so that the operation is almost impossible in such place where the pipe lines are long or curved.
With an attempt to overcome such drawbacks, various improvements were made in both aspects of the pipe-lining method and the lining materials used therein. In an improved pipe-lining method developed for such situations, a flexible tube is inserted into a pipe while turning the tube inside out under pressure of a fluid, such as compressed air and bonded at the same time onto the inner surface of the pipe by the aid of a binder. A method of this type is disclosed in U.S. Pat. Nos. 2,794,785, 3,132,062, 3,230,129 and 3,494,813 and British Patent Nos. 1,002,131, 1,069,623 and 1,025,011. However, these methods were still not satisfactory for the actual pipe-lining treatment for at least one of the following reasons: First, the binder having an extended pot life is required so that the time necessary for the lining treatment becomes inevitably long; Secondly, the quantity and distribution of the binder cannot be controlled so that the binder may be applied unevenly. In addition, the binder must be used in large excess but such excess amount of the binder is, after all, discarded; Thirdly, when the pipe line is inclined, the head pressure of the binder acts on the top or turning point of the tube where evagination occurs so that the pressure fluctuates and the amount of the binder tends to vary. Recently proposed in the above mentioned circumstances are the inventions disclosed in U.S. Pat. Nos. 4,334,943 and 4,368,091 relating to methods and apparatus for lining pipe lines. Especially, the method disclosed in U.S. Pat. No. 4,334,943 is most excellent in the existing pipe-lining methods and is characterized by using a specific rope-like elongated material attached to the same terminal end of the tubular lining material, as another rope-like elongated material and previously passed through the tubular lining material beyond its full length is drawn from the opposite end of the pipe line. As is evident from comparison between FIGS. 4(a) through 4(f) and FIGS. 5(a) through 5( f) given in U.S. Pat. No. 4,334,943, the use of the specific rope-like elongated material drawn from the opposite end of the pipe line is indeed significant in the pipe-lining operation so that the operation can be carried out smoothly without any difficulty as compared with the prior art approaches under a relatively low pressure even in case the pipe line is as long as 1,000 meters or it has a number of curved portions such as bends, elbows and/or offset bends. On the other hand, an improvement has also been made in the tubular lining materials per se with the development of the pipe-lining methods. Initially proposed as a material for lining pipe lines is a tubular plastic material made of a synthetic resin. Such tubular plastic material was directly inserted into a pipe and inflated and bonded onto the inner surface of the pipe by the aid of a binder under inner pressure. However, it was extremely difficult to pass this tubular plastic material directly through a pipe having curved or bent portions. In case this plastic lining material is allowed to pass through a pipe line according to the conventional tube-evaginating method, such plastic lining material tends to broken under pressure when the material is rigid, or alternatively tends to become uneven in thickness under pressure when the material is flexible. In addition, such plastic material is incompatible with a certain kind of a binder so that the binder can hardly be applied evenly onto the whole surface of the plastic lining material. In Japanese Laid-open Utility Model Appln. No. 56-3619, there is disclosed an improved tubular lining material for pipe lines. This lining material comprises a tubular textile jacket with an air-impervious coating of a synthetic resin, which has been knitted or woven in a tubular form with warps and a weft made of synthetic fibers such as polyester filament yarns. This tubular lining material is applied onto the inner surface of a pipe line according to the above-mentioned conventional tube-evaginating method wherein the tubular lining material is allowed to advance within the pipe line and evaginated at the same time under pressure while being bonded to the inner surface of the pipe line by the aid of a binder. In this case, insertion of the lining material into the pipe line is smoothly attained within a short period of time by evagination under pressure and a sufficient amount of the binder is maintained in the interstices of the reticular structure of the textile jacket so that the bonding of the lining material onto the inner surface of the pipe line is assured. In addition, the innermost wall of the lining material is constructed by the air-impervious coating of a synthetic resin as a result of evagination, thus functioning equivalently as a plastic lining material. An elastic polyester resin such as Hytrel (DuPont, U.S.A.) or Pelprene (Toyobo, Japan) is preferably used as the synthetic resin. The warps and weft may be made of other synthetic fibers such as polyamide fibers, vinylon fibers or of inorganic fibers such as glass fibers. A similar tubular lining material is also disclosed in Japanese Laid-open Patent Appln. No. 56-8229, which is applied to a pipe line according to the conventional tube-evaginating methods. This tubular lining material is constructed by a similar tubular textile jacket and a similar coating of a synthetic resin but is stretchable by 10-20% in the peripheral direction and non-stretchable in the longitudinal direction on evagination by pressurized fluid. Because of its stretchability in the peripheral direction, this tubular lining material can easily be inserted into the pipe line and applied onto the inner surface of the pipe line by evagination under pressure. A tubular lining material disclosed in these prior art references is composed of a tubular textile jacket knitted or woven with synthetic fibers and possesses high tenacity in both the longitudinal and peripheral directions. Thus, the material is not damaged when evaginated under pressure and thus has widely been utilized in the conventional pipe-lining methods. In fact, the tubular lining material of this type can be applied to long pipe lines without any problem so far as they are straight. As it lacks stretchability in the longitudinal direction, however, it often forms wrinkles or a narrow flow path in a bend portion of the pipe line where the length of the outer curvature is different from that of the inner curvature, as shown in FIGS. 4(d)-4(f) of U.S. Pat. No. 4,334,943 when used according to a conventional pipe-lining method.
In order to overcome such drawbacks, a new type tubular lining material was recently proposed in U.S. Pat. No. 4,576,205, which is not only expansive in the peripheral direction (i.e. stretchable in transverse direction) but also stretchable in the longitudinal direction. In this tubular lining material, a part or all of warps constructing the tubular textile jacket are comprised of a polyurethane elastic yarn (Spundex yarn) around which, over the full length thereof, a synthetic fiber yarn or yarns have been coiled. This tubular lining material is indeed excellent in biaxial stretchability and applicable satisfactorily to pipe lines with a number of curved portions or bends, showing good compliance with the complicated shape in the curved portions or bends when the lining material is used according to a pipe-lining method as disclosed in U.S. Pat. No. 4,334,943. However, such polyurethane elastic yarns are relatively expensive so that the use of a large quantity of a tubular lining material based on such polyurethane elastic yarns for pipe lines for general use is not advantageous for an economical reason. In general, it is extremely difficult to manufacture a polyurethane elastic yarn of a large diameter. Thus, the lining material proposed in U.S. Pat. No. 4,576,205 has a relatively small diameter and is particularly suitable for reinforcing a pipe line of a relatively small diameter (usually for a service pipe line having a nominal diameter of 1 inch for use in homes, shops and small offices). Considering the nature of such polyurethane elastic yarn, it is rather difficult to manufacture a tubular lining material with a relatively large diameter (larger than 50 mm) from such polyurethane elastic yarns. In addition, the polyurethane elastic yarn is composed of monofilament and becomes inferior in flexibility when processed to a tubular lining material with a relatively large diameter. Further, the polyurethane elastic yarn around which a crimped yarn or yarns of synthetic fibers have been coiled becomes less consistent so that it may not take up a sufficient amount of a binder required for lining pipe lines with a relatively large diameter.
On the other hand, a main city gas conduit or a medium city water pipe generally has a diameter within a range from 50 mm to 400 mm. With a view to preventing pipe lines with such a relatively large diameter from any dangerous burst of gas, water or a combustible fluid caused by unexpected damage of such pipe lines, it is necessary to reinforce such pipe lines with a tubular lining material at least comparable in reinforcing performance with that based on the polyurethane elastic yarn around which a crimped yarn or yarns have been coiled. However, a new economical tubular lining material comparable in quality with that based on the expensive polyurethane elastic yarns and desirable for reinforcing such relatively large pipe lines has not yet been proposed.
Under these circumstances, there is a great demand for developing a new economical tubular lining material which can be applied to pipe lines having an inner diameter of 50-400 mm and a number of bends or curved portions, without permitting occurrence of any wrinkle or narrow flow path in curved or bent portions.